The proposed research will seek to delve into the causal nexus influencing social organization and social behavior in fishes. A series of studies begun during the term of the present grant will be concluded, and several new studies will be initiated. PRoposed research includes: assay of corticosteroid levels in blood plasma of bass in a social hierarchy; investigation of spacing behavior and sensory modalities utilized in social behavior of largemouth bass in clear and turbid environments; an analysis of the behavioral factors contributing to niche differentiation and interspecific competition in centrarchid fishes; the ontogeny of agonistic behavior in blue gouramis, and an experimental study of space use by fish in a "one dimensional universe". A variety of experimental and field techniques are being used to reveal the nature of several proximate causes of social organization and behavior. By evaluating the results of these diverse studies, we hope to focus light on the nature of ultimate causes of social order in teleost fishers, and in so doing provide information useful in phylogenetic analyses of vertebrate sociality.